The present invention relates to a new and improved machine tool and more particularly to an apparatus and method to compensate for deflection of one or more extendible tool support arms.
During the operation of horizontal boring, milling and drilling machines, a ram or tool support arm is commonly extended to move a rotating tool relative to a workpiece. As the ram is extended, the outer end portion of the ram droops downwardly under the influence of gravity. Although the total downward deflection may be relatively small, for example 0.0025 inches for a fully extended four foot ram, even this small error is detrimental to accurate machining. The error increases when a boring bar or second tool support arm is extended outwardly from the ram. A boring bar which is extendible approximately seven feet outwardly from the ram may deflect as much as 0.0152 inches relative to the ram. The total deflection of the fully extended ram and boring bar would be 0.0177 inches. In addition, the total deflection of the ram itself is increased when a relatively heavy right angle drive attachment is connected with the outer end of the ram. Of course the actual ram and boring deflection will be different for different machine tools.
In order to correct for deflection of extendible tool supports, it has been suggested that the saddle or carriage on which the ram is mounted be raised to compensate for the error induced by the downward deflection of the outer end portion of the ram in the manner disclosed in U.S. Pat. No. 3,827,333. This ram deflection compensation method is ineffective to maintain the cutting face of a tool in a desired plane. This is because as the ram deflects downwardly, the axis of rotation of the cutting tool is deflected so that the cutting tool rotates about an axis which is skewed.
It has also been suggested that a brace assembly be utilized to support the outer end portion of the extendible tool support in the manner disclosed in U.S. Pat. No. 3,097,568. Other devices for use in positioning cutting tools having various supporting arrangements are disclosed in U.S. Pat. Nos. 2,798,773; 3,027,813; 3,211,025; 3,233,521; and 3,339,253.